1. Field of the Invention
The present invention relates to an organic light emitting display device, and, more particularly, to an organic light emitting display device capable of achieving an enhancement in light emission efficiency at high current and an enhancement in panel efficiency through prevention of a roll-off phenomenon.
2. Discussion of the Related Art
An image display device, which renders a variety of information on a screen, is a core technology of the information age. Such an image display device is developing toward enhanced thinness, enhanced lightness, and enhanced portability as well as enhanced performance. Currently, an organic light emitting device capable of displaying an image through control of light emission of an organic light emitting layer is highlighted as a flat display device capable of eliminating disadvantages of heavy and bulky structures of cathode ray tubes (CRTs).
Such an organic light emitting device (OLED), which is a self-luminous device employing a thin light emitting layer arranged between electrodes, is advantageous in that it may have a thin film structure such as a paper sheet. In detail, the OLED includes an anode, a hole injection layer (HIL), a hole transport layer (HTL), a light emitting layer, an electron injection layer (EIL), an electron transport layer (ETL), and a cathode.
In particular, an organic light emitting display device is considered an application having competitiveness in that it does not require a separate light source while achieving compactness and distinct color display.
Recently, such an organic light emitting display device employs a white OLED with a stack structure including a first stack structure having a fluorescent blue light emitting layer, and a second stack structure having a phosphorescent yellow-phosphorescent green light emitting layer. In such a white OLED, blue light emitted from the fluorescent blue light emitting layer and yellow light emitted from the phosphorescent yellow-phosphorescent green light emitting layer are mixed, thereby rendering white light.
In this case, the phosphorescent yellow-phosphorescent green light emitting layer may exhibit a roll-off phenomenon in which a reduction in light emission efficiency occurs due to an increase in triplet-triplet annihilation (TTA) exhibited at higher current. As a result, light emission efficiency at high current may be degraded.
A phosphorescent yellow-phosphorescent green wavelength range according to the conventional white OLED includes a green wavelength and a red wavelength. The full width at half maximum (FWHM) according to the conventional phosphorescent yellow-phosphorescent green wavelength range is small, as illustrated in FIG. 1. FWHM means a width at a half maximum height. When the FWHM area is small, the intensity of light according to a green wavelength and the intensity of light according to a red wavelength are reduced. That is, the intensity of light is proportional to the FWHM area. For example, when the FWHM area is small, the intensity of light is reduced. Since the FWHM area according to the conventional white OLED is small, the intensity of light according to a green wavelength and the intensity of light according to red wavelength are reduced, thereby causing a reduction in color reproduction range. As a result, a reduction in panel efficiency occurs.